Transvenous endocardial leads may be placed inside a chamber of a patient's heart by passing the lead through a venous entry site, such as the subclavian vein or the cephalic vein, or a tributary thereof, along a venous pathway into the superior vena cava and into the right cardiac chambers. Coronary or cardiac vessel leads may be advanced further, from the right atrium through the coronary sinus ostium into the coronary sinus and ultimately into one of the various cardiac vessels for stimulation and/or sensing of the left heart chambers.
Cardiac lead placement is important in achieving proper stimulation or accurate sensing at a desired cardiac location. Endocardial or cardiac vessel leads are generally implanted with the use of a guide catheter and/or a guidewire and/or stylet to achieve proper placement of the lead. A cardiac vessel lead may be placed using a multi-step procedure wherein a guide catheter is advanced into the coronary sinus ostium and a guidewire is advanced further through the coronary sinus and great cardiac vessel to a desired cardiac vessel branch. Because the tip of a guidewire is generally flexible and may be preshaped in a bend or curve, the tip of the guidewire can be steered into a desired venous branch. A cardiac lead may therefore be advanced to a desired implant location using a guidewire extending entirely through the lead and out its distal end. Cardiac leads generally need to be highly flexible in order to withstand flexing motion caused by the beating heart without fracturing. A stiff stylet or guidewire provides a flexible lead with the stiffness needed to advance it through a venous pathway. Once the lead is placed in a desired location, the guidewire and guide catheter may be removed. A guidewire placed implantable lead is disclosed in U.S. Pat. No. 6,192,280, issued to Sommer, et al. A coronary vein lead having a flexible tip and which may be adapted for receiving a stylet or guidewire is disclosed in U.S. Pat. No. 5,935,160, issued to Auricchio et al. A coronary vessel catheter or guidewire is disclosed in U.S. Pat. No. 5,509,411, issued to Littmann et al., having a plurality of sense electrode pairs for mapping electrical activity of the heart disposed proximally to a distally extending, manually shapeable, wire coil and core wire distal tip similar to a guidewire distal tip.
Cardiac vessel leads are particularly difficult to implant due to the tortuous pathway encountered as the lead is advanced through the cardiac vessels. Because of this difficulty, the surgical time required to implant a cardiac vessel lead can be considerably longer, up to 1 to 2 hours longer, than the time required to implant an endocardial lead in a right heart chamber. Placement of a cardiac vessel lead in a desired venous branch may require angling the lead end greater than 90° in order to maneuver it into the branch. Some cardiac vessel locations may therefore be inaccessible due to limitations and difficulties associated with maneuvering currently available lead systems into a narrow venous branch at an oblique, or even acute, angle.
It would be desirable, therefore, to provide a cardiac vessel lead having the physical properties needed for advancing it through a venous pathway to a desired implant site, particularly within the cardiac vessels, without the need for additional guide catheters or guidewires. The number of instruments and steps required to perform a cardiac vessel lead implantation procedure could then be reduced, making the procedure easier to perform and reducing the associated surgical time and cost.